1. Field of The Invention
The invention relates to the field of separation methods and devices for separating flat parcels, such as letters, documents and the like, from a stack, and in particular to an apparatus and method using a drawing element that travels in a conveying direction and acts by means of friction on a respective parcel to be drawn off.
2. Background Information
Separation methods and devices are known from, for example, European Patent EP 0,142,538. One known problem associated with separation methods and devices is the so-called double-drawing error. This error occurs when in addition to a desired first parcel to be drawn off of a stack, a further second parcel is drawn off. This problem may be due to the frictional force between the first parcel in the stack and the second parcel being too great, or because the second parcel protrudes and is drawn off too early due to an insufficiently uniform alignment of the front edges of the parcels.
A further problem lies in controlling a clearance gap between the drawn-off parcels, which is determined by the force exerted by the drawing element on the first parcel in the stack. Both of these problems, i.e., the double-drawing and clearance gap problems, are to a degree functions of parameters such as the parcel features, i.e., particularly weight, thickness, roughness and moisture content of the parcel material, as well as environmental conditions, in particular the amount of moisture in the ambient air.
A further problem associated with known separation methods is that a considerable amount of paper abrasion can be caused by the drawing element, which can lead to particulate accumulation in the separating device and to environmental pollution.